Polylysine: An Activator of Smooth Muscle Contractility

Abstract

Polycationic amines are known to affect a wide variety of biochemical reactions and have thus been used as probes of mechanism in cell-free systems and isolated cell fractions (Ahmed et al., 1986; Gröschel-Stewart et al., 1989). Polycations are of particular interest to the study of the mechanisms of regulation of contractility in smooth muscle for they are reported to be modulators of phosphoprotein phosphatases (DiSalvo et al., 1985). Phosphatases play a major role in the control of the level of myosin light chain phosphorylation, which in smpoth muscle is the primary transduction mechanism for regulation of contractility (Hartshorne, 1987). A specific phosphatase inhibitor would be of interest not only in terms of the mechanism of crossbridge regulation, but also in terms of identification of the nature of the physiologically relevant phosphatase in smooth muscle. We have thus studied the effects of polylysine on the contractility and ATPase activity of “skinned” (permeabilized) smooth muscle fibers and ATPase activity of smooth muscle actomyosin. For comparison we have also studied the effects of polylysine on actomyosin prepared from skeletal muscle.